Followup: The problem was that little extension cable that brings the ECT sensor connection out from under the AC compressor - the wires had gotten old and hard and fatigued at the crimps. So the ECU was seeing it as disconnected and failing to advance the timing. It's settled down now and is running pretty well, and I'm free of CEL codes (that speed sensor code hasn't reappeared).

Which leads me to a couple of new questions.

First, when it's really loaded - pulling the horse trailer at highway speed up hills on a hot day - it's working hard and the engine temp is high. Still within the gauge's "normal operating range" marks, but just barely. What steps can one take to enhance heat dissipation? I've heard about surfactants (wetting agents) that are added to engine coolant to increase cooling efficiency - do they actually help or are they just pixie dust?

Second (and I appreciate that this invites a larger discussion), what are the best (i.e. cheapest and easiest) mods for increasing power from this beaten-up old 318 TBI?

 

First - 1) Make sure the cooling system is in tip top shape. If you can find a boneyard truck with the Extreme Cooling or Max Cooling radiator and shroud, buy that shroud. Shucks, if it's an all metal radiator, buy that, and get it rodded and rebuilt at a competent radiator shop! (Since I bought mine from RockAuto, the new ones are plastic tanked. They work, but it's hard to get them fixed when the tank cracks. )

2) Add a transmission oil cooler ... I did one instead of the in-radiator one, but you may want to run in series. Use the parts diagram for the sequence for the towing package auxillary cooling unit, even if you use a new one. I'd also go for a stacked plate design; they tend to self regulate and not overcool as much as a bent-tube design can.

For the second - Save up and upgrade to a Magnum with SEFI/MPFI. Best thing you can do. Past that, upgrade to a Ram 360CID/5.9L out of a TBI RAM.

Don't forget to keep it tuned up.

Well, you can bump the timing some on the LA TBI units; if you go as high as 14* BTDC or even 16, it wakes it up nicely, but the crap combustion chamber design means it'll be more prone to preignition on regular fuel, so you'll want to upgrade to mid-grade or even premium.

That's about it until you tear into the motor, upgrade the pistons, upgrade to Magnum heads, upgrade the camshaft, get a tuneable ECU, etc.

RwP

 

Okay, I had to go take a look at the truck (down the road at the stable) to refresh my memory on this. I replaced the (factory, metal) rad about ten years ago when it was running too hot under much less demanding conditions than I'm dealing with now - it had just gotten too clogged up, I guess. The replacement (which is in there now and appears to have an internal tranny cooler) was/is a junkyard rad, and plastic, though it does have a shroud. I kept the old rad (with the external tranny cooler) as a matter of course, since I'm an unreconstructed pack rat. So perhaps there'd be an advantage to me if I had the old one rebuilt. I know what recoring is, but what is "rodding"?

And I have no idea what an "Extreme Cooling or Max Cooling" rad is. How would I tell one if I saw it?

That's so not going to happen. This is a rusty old farm beater 4x4. I want to get the best/cheapest use out of it, but it doesn't interest me as a project or investment.

Goes without saying.

Okay, that's good to know, but what does "LA" mean?

As I said, just looking for the best possible modest gains for equally modest bucks/time/effort.

 

"Rodding" a radiator is when they use rods to clean out the core tubes. Strange that it's actually what it says on the tin, I know.

The Extreme Cooling or Max Cooling (both had the same parts, different year and package definition) is the widest radiator that will fit in the 1st Gen trucks from the factory. The shroud had three "doors" on the back to let air vent through when moving down the road, but closes at idle to force the air from the radiator past the fan.

I understand about the beater *grins*

And "LA" means "Light A", it's the motors designed to replace the "A" motors back in the 1960's. The more common V8s were the 273, 318, 340, and 360. The 3.9 is basically a 318 with two cylinders lobbed off, and the crank redressed to make it uneven fire. (The 3.9 can use the same pistons, rings, valves, valve springs, and main bearings; the 318/5.2 rods need to be dressed either .030 or .060 to clear the offset throws of the 3.9 - I don't remember if it's .030" total, or .030" each side.) They were replaced in the 1992 model year in the Dakota with the Magnum designs. Magnums breath a LOT better, but are also MPFI or SEFI, not TBI. Le sigh. (Intake/Head bolts are also different, so you can't just swap an intake between them. There's other considerations in mixing parts, too.)

RwP